The cellular industry is constantly seeking new ways for improving how people are able to communicate. With the introduction of EDGE (Enhanced Data rates for GSM Evolution) technology for GSM (Global System for Mobile communication) and the HSPA (High-Speed Packet Access) for WCDMA (Wideband Code Division Multiple Access) the data communication in cellular terminals has reached new heights. The so-called IMS (IP Multimedia Subsystem) has given new opportunities to create additional interesting IP (Internet Protocol) based services, such as Push-to-talk Over Cellular (PoC). MBMS (Multimedia Broadcast Multicast Service) [1] is yet another feature that allows for efficient deployment of broadcast and multicast services, such as mobile TV or PoC group communication. This is a fact since MBMS offers true broadcast and multicast even over the radio. For example users, or actually the mobile terminals, in e.g. GSM/(E)GPRS would listen to the same time slots carrying the MBMS data channel
Basically, MBMS (Multimedia Broadcast Multicast Service) is an IP datacast (IPDC) type of service that can be offered by e.g. GSM and UMTS cellular networks. The infrastructure of those networks gives the possibility to use an uplink channel for the interaction between the service and the user or mobile terminal. A broadcast service can be generalized to mean a unidirectional point-to-multipoint service in which data is transmitted from a single source to multiple mobile terminals (MT) in an associated broadcast service area. In other words, broadcast services can be called push-to-talk-type services. On the other hand, a Multicast Service can be defined as a unidirectional point-to-multipoint service in which data is transmitted from a single source to a multicast group in its associated multicast service area. Only the users that are subscribed to the specific multicast service and have joined the multicast group associated with the service can receive the Multicast Services.
With the above in mind, and the fact that an important part of Public Mobile Radio and Public Safety Radio (PMR/PSR) services is group communication, it is obvious that cellular systems used for traditional mobile tele- and data communication are potentially developing into highly attractive alternatives to the analogue PMR/PSR systems, used by e.g. police departments, fire departments and security and transport companies.
In essence, group communication as it will be used in this disclosure concerns mainly multicast sessions where one user speaks or transmits information e.g. data files, video broadcast etc. to a plurality of other users that merely listen or receive information. It is a highly asymmetrical service where the speaking user only uses a small uplink resource, whereas the listeners collectively use many downlink resources. Especially, the situation where a large group of listening or subscribing users or mobile terminals are located within a same limited area or geographical location, e.g. construction site, residential area, coffee shop, accident site, airport etc. The speaker wants to transmit crucial information in an efficient manner.
One service included in a PMR system based on commercial available cellular technologies, as given above, would be PoC using MBMS to support large communication groups. This would enable an attractive PMR/PSR service highly useful for example police, firefighters, taxi drivers etc.
However, there are a number of issues that needs to be resolved. One major issue is the resource consuming paging procedure that is necessary in order to locate the various mobile terminals participating in a multicast session. Especially, for relatively large number of mobile terminals subscribing to a multicast session. Each mobile terminal receives a paging message from the network and is required to respond in order to provide location information, e.g. in which cell or to which node in the network the mobile terminal is currently located. The paging message from the network consumes little resources, but a large number of mobile terminals each responding to the paging message consumes plenty. One of the consequences is the introduction of delay since the network needs to wait for all subscribing mobile terminals to respond to the paging message.
Consequently, there is a need for methods and arrangements to reduce the paging introduced delay and enable efficient multicast group communication in a MBMS enabled network.